Permanganate in the Presence of Ferric Chloride. 33 



ing 36*4575 grams of the acid to the liter), and in addition either 

 9'91 cm3 of tenth normal hydrochloric acid (prepared by diluting 

 100 cmS of the normal solution to one liter) or 9 , 91 cm3 of tenth 

 normal ferric chloride. Of approximately twentieth normal 

 potassium permanganate, carefully standardized against ammo- 

 nium oxalate, 9"91 cm3 were then added, and the flask, fitted in a 

 ground joint to a return-condenser 60 cm in length and with 

 a bore approximately 3 cm in diameter, was heated for one 

 hour in the Ostwald thermostat at a temperature of 50° C. 

 Of tenth normal oxalic acid, 9'91 cm3 were then added to the 

 digestion liquid and a measured volume of the same perman- 

 ganate solution as was added before digestion was run in to color. 

 The difference between the total permanganate used (that is 

 the permanganate added before digestion plus that added to 

 bring about final coloration against the oxalic acid) and the 

 permanganate equivalent of the oxalic acid added gives, accord- 

 ing to Wagner, the permanganate reduced during the diges- 

 tion. The results of these experiments are recorded in the 

 above table. 



Here it may be seen that although in general more perman- 

 ganate is required to bring about final coloration in those experi- 

 ments in which ferric chloride was used than in its absence, the 

 results show at best wide variation among themselves, and the 

 amounts of permanganate apparently destroyed during the diges- 

 tion are at all events considerably greater than in the experiments 

 conducted by Wagner under similar conditions. In the experi- 

 ments recorded in Table I, in the average 4*73 cm3 of per- 

 manganate were apparently destroyed where ferric chloride was 

 not used, and 5 , 37 em3 in the presence of ferric chloride; while 

 in Wagner's experiments 0'96 cm3 of permanganate was appar- 

 ently reduced without use of ferric chloride and l-4l cmS in its 

 presence. 



Since, as has been noted above, the permanganate color 

 entirely disappeared in the experiments of Table I, long before 

 the termination of the hour's digestion, while only small amounts 

 of hydrated oxides of manganese varying in color from brown 

 to black were visible in the digestion liquid, it seemed probable 

 that more permanganate was really reduced during the digestion 

 than is indicated in these experiments. Moreover a strong 

 odor of chlorine was noticeable in these experiments and it 

 seemed probable that some of the chlorine, formed by the 

 interaction of the potassium permanganate and hydrochloric 

 acid during the digestion, remained to take part in the oxidation 

 of the oxalic acid introduced, and that, therefore, on running in 

 permanganate solution to color, less of the latter was required 

 than corresponded to the oxalic acid left unoxidized by the 

 residual oxides of manganese. It was, therefore, decided to 



Am. Jour. Sci. — Fourth Series, Vol. XIX, No. 109. — January, 1905. 

 3 



